Direction finder antennas



Oct. 27, 1959A A TROOST EIAL 2,910,695

DIRECTION FINDER ANTENNAS Filed March 26, 1957 4 Shee'cs--Sheety 1 l l gl Prior Aff Ct. 27, 1959 A, TRQos-r ETAL 2,910,695

DIRECTION FINDER ANTENNAS W .[m/e/vvrs A. TROOST ETAL DIRECTION FINDER ANTENNAS Oct. 27, v1959V 4 Sheets-Sheet 5 Filed March 2e. 1957 Oct. 27, 1959 A. TROOST EI'AL 2,910,695

DIRECTION FINDER ANTENNAS United States Patent O f' DIRECTION FINDER ANTENNAS Albert Troost and Gnter ziehm, Ulm (Danube), Germany, assignors to Telefunken G.m.b.H., Berlin, Germany Application March 26, 1957, Serial No. 648,610

Claims priority, application Germany March 28, 1956 18 Claims. (Cl. 343-855) The present invention relates to a direction iinder antenna system and, more particularly, to direction iinding antenna systems by which the reception of spurious signals is rendered negligible.

It has been known to reduce or eliminate direction finding errors occurring in direction finder apparatus due to reflection fromobstacles by.connecting the directional antenna to the direction iinder apparatus via a relatively long cable and to place the antenna as high as possible and remote from the reflecting obstacles.V Thus, itV has proven advantageous in case of direction finder apparatus on shipsto mount the antenna on the mast-head.

VHowever, such arrangement results in spurious currents in the directional antenna because the latter, together with the long antenna cable and/or mast, represents a linear antenna. In such linear antenna arrangement, currents are induced which are multiples of the currents flowing in the directional antenna, particularly, if the length of the linear antenna is in theorder of a quarter of the operating wave length. The difference between the actual directional antenna current and the spurious currents will be apparent by comparing the effective height of a directional antenna which, in the medium wave range is only a few4 centimeters, with the effective height of a linear antenna, the length of which amounts approximately to a quarter of the operating wave length,

Y i.e., in the order of 100 m. Thus, the ratio of the spurious current to the directional antenna current mayV amount to a factor of about 2000 in the medium wave range.

It is an object of the present invention to provide an antenna which is insensitive to spurious currents caused by the antenna system acting as a linear antenna in combination with a long cable or with a mast on which the antenna frame is mounted. The spurious currents must Yalso be rendered ineffective if the transformer at the input from the antenna or at the receiver input is unsymmetrical.

It is another object of the invention to produce a directional antenna which is divided into two, Vpreferably equal, halves disposed in parallel planes or in a single plane, whereby the terminals of these antenna halves are interconnected and are arranged in such a way that the directional currents induced in the two halves of this antenna are additive in a cable connected to the common terminals, while the spurious currents of the linear antenna induced in the corresponding halves are cancelled in the direction of the polarization of the radiation.

It is a further object of the invention to provide as preferred embodiment of the invention an antenna having two halves arranged one upon another in a common plane, whereby the terminals are disposed facing each other on adjacent sides of the halves.

Direction finder antenna systems in which an interconnection of two antenna sections is provided have been known and comprise two vertical dipoles which are in terconnected to oppose each other. In this case, the system is intended to absorb only the vertically polarized 2,910,695 Patented Oct.V 27, 1959 ICC components of the radiation reaching vertically disposed dipoles. Horizontal antenna elements are'intentionally avoided in this system, i.e., they are connected to oppose one another in such away that the voltages induced therein are cancelled.

In contrast to this known direction finder antenna system, it is a still further object of the present invention to provide a directional antenna having two halves, each of which constitutes a closed loop which, obviously, requires horizontally disposed interconnecting members.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood however that the detailed description and specie examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawings:

Figure 1 is a diagrammatic representation of a directional loop antenna and matching transformer feeding a balanced shielded cable, according to the prior art;

Figure 2 is a diagrammatic representation of-a novel antenna circuit and matching transformer, according to the present invention;

Figure 2a is a diagrammatic representation of an antenna circuit similar to that of Figure 2, but differently proportioned as to the relative size of the loops;

Figure 3a is a diagrammatic, perspective viewv of an embodiment of a dual antenna system employing two antennas of the type shown in Figure 2, but displaced 90 `with respect to one another and showing a nondirectional auxiliary antenna;

Figure 3b is an enlarged View of details of the central portion of the antenna system shown in Figure 3a;

` in the following with reference to Figure l.

voltage to a higher value.

The` input terminals oi 1a directional antenna 1 are denoted by 2 and 3. A primary Winding 4 of a transformer 5 is connected to the input terminals 2 and 3, said transformer 5 being used to transform the antenna A secondary winding 6 of the transformer 5 is connected to the input of a shielded twinl conductor 7, feeding the antenna voltage to the receiver input. As long as the plane of the direction iinder antenna is not perpendicular with respect to the transmitter, a directional current ip is induced in the antenna by magnetic induction, said current at a given time Howe ing in the direction indicated in Figure 1 by the arrow. Due to the fact that the antenna together with the antenna conductor or the shipmast on which the antenna is mounted form a linear antenna, spurious currents is are induced in vertical elements of the antenna, said spurious currents being of the same intensity and, in the minimum position of the antenna, of the saine phase, and of a multiple value of the antenna current ip, as mentioned in the foregoing. if the combined antenna and transformer 5 are perfectly symmetrical, then the currents is become ineffective because, since they have the same magnitude and are of the same phase, they will act with the same intensity in the primary winding 4 of the transformer 5, and will be conducted to ground via the center tap without exerting any influence on'the secondary winding '6 and, therefore, on the receiver input. In this minimum position, the current iP becomes zero, since the area of the plane coupled with the magnetic field also becomes zero.

The, condition that the antenna together with the transformer are designed exactly symmetrically is almost impossible. The antenna itself may be made almost symmetrical at reasonable expense; however, it is practically impossible to manufacture a transformer without an error in symmetry. It will be readily understood that the spurious currents is are not completely cancelled in case of a less than symmetrical construction of the transformer 5, and they will act on the antenna cable 7 producing a voltage at the receiver input at the position of minimum directional signal energy, whereby this voltage causes obscuring of the position of the minimum directional signal.

Embodiments of theinventive antenna systems will be :described in the following:

VFigure 2 shows a simple and therefore particularly clear embodiment of an antenna system according to the invention. This antenna system comprises two symmetrical halves 8 yand 9 disposed in one plane. The two terminals lie in the adjacent parts in these two symmetcal halves. The input terminals of the half-antenna 8 are denoted by and 11 and the input terminals of the half-antenna 9 are denoted by 12 and 13. The input terminal 10 is connected to the input terminal 13 and the input terminal 11 to the input terminal 12, via short connections. The primary winding 14 of a transformer 15 is connected across the terminals 12 and 13, said primary winding being provided with a center tap which is connected to ground in the known manner described With reference to Figure 1. The' secondary winding 16 of the transformer 1S is connected to an antenna cable (not shown) or directly to the receiver input. The secondary winding 16 also is advantageously provided with a center tap for connection to-ground.

The operation of this system is as follows: As in the known system, the directional currents ip flow at a certain instant in a clockwise direction, as indicated by the arrows. The two directional currents ilow at said instant in the antenna halves S and 9 from the terminal 13 to the terminal 12 and from the terminal 12 via the primary winding 14 of the output transformer 15 back to the terminal 13. Therefore,` the ytwo currents ip are adding in the primary winding at any instant of time, except when the antenna is adjusted to minimum signal position. In addition to the directional currents, equally large spurious currents is are induced in the vertical elements of the antenna which are attributed to the fact that the directional antenna together with its cable acts as a linear antenna. In the minimum signal position, all of the currents is are of the same phase. As shown by the dashdash lines having arrows, at the minimum signal position of the input terminal 12, a spurious current is flows via the terminal 11 from the right vertical element of the half 8 to the same terminal and from there a current of the same value and the same phase flows in the left vertical element of the half 9. Due to the fact that these two currents are of the same phase, no spurious current can flow in the minimum signal position of the antenna from the terminal 12 to the primary winding 14 of the transformer 15 since, obviously, the following condition has to be fulfilled for any particular network terminal at any given instant:

The total of all of the currents flowing to such terminal must be equal to the total flowing away therefrom.

The same is true for the input -terminal 13, where the spurious currents flowing from the left vertical element of the half 8 via the terminal 10 equal the spurious currents flowing into the right vertical element of the half 9.

An additional effect is obtained by interconnecting the halves 8 and 9, this effect consisting of a reduction in the tptal inductance of the antenna according to the invention with respect to that of a conventional directional antenna. Thus, a decrease in inductance by a factor of 2:1 `is obtained by this interconnection. Furthermore, the interconnection of the terminals'of the two halves results in causing the mutual inductance of the magnetic iiux crossing the halves 8 and 9 to act in opposite directions, thereby resulting in a further decrease in the total inductance. The following formula is obtained for this total inductance:

wherein L is the inductance of one half of the directional frame and k is the coupling factor between` the halves 8 and 9. The factor 1/2 in front of the bracket is due to the interconnecting, the minus sign in front of the coupling factor k is dueto the coupling of the ux of the two halves 8 and 9 in opposite directions. In a practical directional antenna according to the invention, the coupling factor k between the halves 8 and 9 is approximately 40%, so that a decrease in inductance of the antenna by a'factor of 3:1 is obtained as compared with the conventional directional antenna of Fig. l.

Furthermore, it should Vbe mentioned that the directional current in the primary winding of the transformer is increased by a factor of 2:1, due to the additive effect, so that the ratio of the no-load voltage to the inductance of the directional antenna as compared with a conventionalantenna will be increased by a larger factor. In this case, a directional frame is improved, the higher the no-load voltage and the smaller the inductance. In this connection, it is apparent that the useful area of the directional antenna, according to Fig. 2, is twice as large in the selected example of the conventional system according to Figure 1.

As a result of the decrease in the inductance of the antenna, the inductance of the primary winding 14 and, thus,'the inductance of the secondary Winding 16 of the transformer 1S can be correspondingly decreased. Thus, an improved symmetry of the outputtransformer is obtained because the symmetry of the transformer, as practical experience shows, is improved as the inductances of the transformer are decreased; The fact that with decreasing antenna inductance, the inductance of the primary winding 14 canV also be decreased, is derived from the fact that the inductance of the primary winding 14 must always be much larger than vthe inductance ofthe antenna to prevent too large a voltage division between the antenna inductance and the inductance of the primary of the transformer.

If the radiated field causing the energization of the undesired linear antenna is not homogeneous, the current ig inthe individual parts of the directional antenna willbe different in case of absolute symmetrical design of the two halves, so that no complete cancellation of the currents is of the two halves occurs in the antenna minimum position. However, a complete cancellation can be obtained if in such case at least one loop 8 is made with different vertical dimensions in such a way thatthe currents is in the two halves have the same values. Such an antenna is illustrated in Figure 2a.

The neutral element of the half antennas, which are respectively located diametrically opposite the terminals of the halves 8 and 9, are advantageously connected to ground, whereby'the action of unequal coupling capacities is rendered harmless. Also, the mounting of the directional antenna is facilitated because the frame is firmly attached at such points to a grounded supporting means, for example, a metal pipe.

lObviously, the halves may have other shapes than the design shown in Figure 2, i.e., they may comprise several turns and have circular cross sections.

Furthermore, it is possible to design the halves as ferrite antennas. p f

The halves gccgrding t9 the `system of Figure 2 donot have to be arranged in a single plane. It is even possible to displace the upper half parallel towards the front or the rear or towards the bottom, so that the planes of the halves are always parallel. In this case, however, the

Vconductors between the inputs of the two halves would have to be longer than in the system illustrated in Figure 2. In the embodiment of the invention shown in Figures 3a and 3b, a directional antenna designed for interconnection is illustrated. A so-called crossed loop construction is used in this embodiment. As in known crossed loop structures, the antenna according to the invention comprises two composite antennas disposed in two vertical planes, which are perpendicular with respect to one another, wherein the `directional antennas are advantageously designed according to Figure 2. The upper part of one of the directional antennas comprises two elements 17 and 18 forming part of a cylindrical wall and being highly electrically conductive. These elements of the directional antenna are vertical and form with a top plate 19 of similar cross section the antenna loop. The lower part of the associated half antenna lying in the same plane comprises in an analogous manner the elements 20 and 21 as well as the lower circular plate 22. The second directional antenna displaced 90 in a vertical plane comprises in exactly the same manner an element 23, partially broken away in Figure 3a, an element 24 and an upper plate 19, as well as the elements 25 and 26 and the lower plate 22 below the upper elements. A cylinder of insulating material, such as a polyester compound, is provided to mount the elements ofV the antenna, said cylinder being closed by the plates 19 and 22 on its upper and lower ends, respectively. The elements may be embedded in the wall of the cylinder or they may be attached to the inside thereof. In such case, the elements may be made of thin metal foils.

A metal pipe 37 is provided in the axis of symmetry of the cylinder formed by said elements, the metal pipe being conductively connected to the plates 19 and 22. The pipe 37 receives the antenna cable and carries a hollow casing 32 at its center. This casing 32 contains two transformers adapted to transform the antenna voltages to higher voltages flowing in the lead-in cables and, furthermore, serves to shield the transformers from the antenna system.

Interconnection conductors 27 to 3i) are provided in the embodiment of Figure 3a, corresponding to the connections between the terminals 10 and 13 as well as 11 and 12 in Figure 2. Since the details of the center portion of the antenna according to the invention with particular reference to these conductors cannotbe recognized in Figure 3a, this portion is illustrated on an enlarged scale vin Figure 3b, clearly showing the pipe 37 and the casing 32 containing the symmetry transformers. Only four elements, i.e., 17, 18, 2u and 21 of the eight elements of both antennas are illustrated in Figure 3b,

the strips to the ring 31. The center point 33, `at the exact center of the metallic strip 27, and the corresponding center point of the metallic strip 28 on the opposite side (not visible in the Figure 3b) are connected with the4 primary winding of a transformer. The secondary winding of this transformer forms the input for shielded parallel conductors 35 which feed a goniometer eld coil. The primary Winding of the other transformer is connected with the conductor strips 29 and 30 in an analogous manner, the secondary winding of thisv transformer also feeding a shielded parallel conductor 36. The parts of the `conductors 35 and 36 are illustrated in Figure 3a at the lower end of the pipe 37. A further metal casing 38 is provided on the upper end of the pipe 37 above the plate 19, said casing 38 supporting a linear antenna 39. This linear antenna 39 serves to obtain a non-directional component of radiated voltage required for sharpening the direction finding. A transformer is provided in the casing 3S, transforming the grounded unsymmetrical voltage produced in the antenna 39 into a symmetrical voltage, which is fed to the'receiver input via a shielded two-Wire conductor 4@ which is partially shown at theV lower end of the pipe 37 in Figure 3a.

While it is possible to feed the voltagel from the linear antenna 39 to the receiver input via a coaxial cable, it

is recommended to make the cable for the linear antenna v voltage of the same length or at least of the approximate length as the cables 35 and 36, carrying the directional voltages. Indeed, the phase difference between the nondirectional voltage of the auxiliary antenna `39 and the directional voltages has to be always constant. However, this requirement seldom can be fulfilled with different kinds of cables, because cables which are substantially different from one another shift the phase of a particular wave to a different extent per unit of length.

In order to protect the antennas from weather, such as ice and snow, it is recommended to provide above the linear auxiliary antenna 39 a bell-shaped hood, for example, of polyester, whereby preferably this hood covers the whole plate 19. A horizontally arranged bracket may be provided to Vmount the antenna system, for eX- ample on a masthead, said bracket being bolted to the bottom plate 22 of the antenna.

In the embodiment of Figure 3a, the spurious currents f in the directional antenna are rendered harmless. Howthese elements being associated with the antenna in onej plane, namely the plane of the drawing.

For the sake of clarity, the segments associated with the other directional frame are omitted in Figure 3b. Since the casing 32 is grounded and contact between the conductors carrying current and the casing 32 should be avoided, a -ring 31 is placed over the center part of the casing 32, said ring being made of insulating material. It is recommended to select the thickness of this ring 31 so that capacities between the casing 32 and said con ductors are negligibly small. The elements 17 and 2t? are joined via the metallic strip conductor 27, the central section of which is placed around nearly half of the circumference of the ring 31. The outer sections of the conductor strip 27 between the ring 31 and the elements are twisted in each case 90 with respect to their longitudinal axes insuch a manner, that the length dimension of the cross section at the ring 31 is always vertical at the points of connection, and horizontal at the elements.

ever, spurious currents, caused by the undesirable formation of a linear antenna by the directional antenna together' with the antenna cable or mast, may also occur in conventional rod-type auxiliary antennas. Spurious currents in the auxiliary antenna prevent the amplitude of the non-directional lvoltage from being determined by the length of the auxiliary antenna itself, but allow it to be determined by the whole electrical length of the vertical antenna system comprising the mast, the directional antenna and the auxiliary antenna. Thus, the same antenna installation, when mounted on masts of different heights, furnishes different amplitudes of non-directional voltages at the same frequencies. Besides, the non-directional voltage derived from such auxiliary antenna would, to a great extent, be frequency dependent, due to reasonance effects. Further disturbances occur, because the Vphase of the non-directional voltage varies, particularly in the neighborhood of quarter-Wave resonance of the linear antenna system from to +90". The determinationof the directional by means of a cardioid diagram is feasible only in cases where the phaseof the broadcast voltage is ,exactly the same as the phase of the directional voltages.

Therefore, an auxiliary antenna system is proposed to avoid these disadvantages,wherein this system furnishes a non-directional voltage which is insensitive to disturbances. Such auxiliary antenna system is characterized by at least two shunted dipoles which are arranged in pairs on opposite sides of the vertical axis of symmetry of the directional antenna.

An example of a modified auxiliary antenna system according to the invention is illustrated in Figure 4. This auxiliary system comprises dipoles 41 and 42. Only the contours of the directional antenna 43 are indicated in Figure 4, i.e., the details of the directional antenna'have been omitted for the sake of clarity. The two dipoles 41 and 42 are arranged on opposite sides of the vertical axis of symmetry of the Adirectional antena. The upper and the lower halves of the dipoles are shunted on the same sides via connecting conductors running horizontally. The interconnected halves of the dipoles are connected to the primary winding of a transformer 44. The secondary winding of this transformer 44 is connected to ground via a center tap, while the two terminals of the same lsecondary winding are connected to an auxiliary antenna cable 45 which, in the present example, constitutes a shielded two-wire cable.

To facilitate the understanding of the operation of the auxiliary antenna system according to the invention, the various currents flowing in the halves of the dipoles are indicated by arrows along -the vertical dipole portions. The actual, useful currents which are proportional to the non-directional voltage are indicated by the' arrows in full lines. These currents may ow at a certain instant downwardly. Since the directions of the useful currents in the upper dipole halves as well as in the lower dipole halves are always the same, these currents will be added to one another in the primary winding of the transformer in case of dipoles shunted in accordance with the invention. The spurious currents at the instant considered ilow in the direction indicated by the dash-dash arrows. These currents flow in oposite directions to ground via the primary Winding of the transformer 44 and via the coupling capacities always present, whereby in case of absolute symmetry, no voltage will occur in the secondary winding of the transformer. Since the upper and the lower dipole halves are slightly diiferent, due to different capacitive coupling with the mast and thereby with the ground, a spurious Voltage remains in the secondary winding of the transformer 44, said spurious voltage corresponding to the difference of spurious currents in the upper and lower dipole halves. The primary Winding is advantageously connected to ground because an adjustable tap in the winding of a transformer to cancel the asymmetry present is not practical. A differential condenser 46 is preferably provided for balancing of the upper and lower dipole halves, the adjustable plate of this condenser being connected to ground. The asymmetries of the dipole halves are balanced by suitably adjusting the diiferential condenser 46 so that the spurious currents indicated bydash-dash arrows in Figure 4, owing to the differential condenser, are exactly equal. These currents flow through the primary winding in opposite directions and, thereby, produce no voltage at the output of the transformer 44. For the currents in the upper dipole halves, as known from experience, are greater than those of the lower dipole halves, balance can be obtained by connecting the terminals of the upper dipole halves with the primary winding of the transformer 44 which is connected to ground via a condenser, preferably adjustable. If properly adjusted, the current owing to ground via this condenser is of such value that the spurious currents flowing in the primary winding in opposite directions are of the same value. This compensating device has no effect on the useful currents which flow through the primary winding in the same direction.

, A further possibility for obtaining absolutesymmetry of which only the dipoles 54, 55 and 56 are visible.

of the spurious currents of the upper and lower dipole halves may be obtained if the-dipole halves are made of different length and/or different shape.

The construction of an antenna according to the invention by application of an auxiliary antenna system is illustrated in Figure 5. The dash-dash lines indicate the upper `end of a shipmast 47, and a horizontal plate 48 welded thereto, on which plate the directional antenna is mounted. The antenna shown in Figure 5 is distinguished from the antenna in Figure 3a in that the vertical elements are made of conductive pipes rather than of sheet material. Of the crossed directional antennas one can see the vertical elements 49 and 50, but two further vertical elements of these antennas are hidden behind other conductor parts. An electrically conducting metal pipe 51 is disposed as an extension ofthe shipmast along the vertical axis of symmetry of the antenna system. The antenna cables run in the lower half of this pipe 51 which constitutes a ground connection between the neutral points of the directional antennas. A dome-shaped plate 52 is provided according to Figure 5 to electrically connect the upper ends of the vertical elements 49 and 50 with two further vertical elements of the antenna, not visible in this figure because they are arranged behind the elements 49 and 50. The lower ends of the vertical elements of the antenna are electrically connected with one another via a plate 53. The plate 53 is advantageously made of the same shape as the plate 52 for reasons of manufacture. The auxiliary antenna system according to the invention comprises four vertically disposed dipoles, The fourth dipole is disposed exactly behind the dipole 5S in the illustration shown in Figure 5. The four dipoles are mounted on a casing 57 by means of heavy connecting pieces 58 to which the cylindrical pieces 59 surrounding the dipole terminals are welded. The connecting pieces 5S, the cylindrical pieces 59 and the casing 57 are made of a weather-proof insulating material, such as polyester. The cross connections between the symmetrical halves of the directional antenna frames and the matching transformers and symmetry-balancing members of the directional antenna and the auxiliary antenna systeml are housed in the casing 57.

In the example of Figure 5, the auxiliary antenna dipoles are disposed symmetrically with respect to the crossed antennas, or, in other words, the auxiliary antenna dipoles are located on the bisectors of the angles between the planes of the directional antennas. Such symmetrical arrangement of antennas and auxiliary antenna dipoles is recommended for reasons of design, although any angle position of the auxiliary antenna arrangement with respect to the antenna surfaces of the di- .posed necessarily at the same height as the directional antennas, i.e., it may be arranged, for example, above the directional antennas. However, this system is less recommended in view of electrical considerations, because in such case, the dipole halves, as a result of the different distance from the directional antenna, would be loaded asymmetrically to a relatively great extent by the spurious vertical currents.

We claim:

l. A directional antenna system including at least one set of paired halves, serving to receive desired directional signals and to suppress signals spuriously received in the minimum position of the directional antenna to the extent that said paired halves operate as a compositelinear antenna, said paired halves comprising two loops each having at a location adjacent the other loop two terminals and each loop having at a location symmetrical with respect to its terminals a grounded center tap, two conductors each connecting diagonally opposed terminals of the two loops together; and coupling transformer means having at least one winding connected between said conductors and having a grounded center tap.

2. In a system as set forth in claim l, the loops of each set of paired halves lying in parallel planes.

3. In a system as set forth in claim 1, the loops of each set of paired halves lying inthe same plane.

4. In a system as set forth in claim 1, the elements of the loops of said system operating in a nonuniformly illuminated field and those elements disposed in the direction of polarization of said field being adjusted in size with respect to one another to compensate for said nonuniformity.

5. In a system as set forth in claim l, the loops of each set of paired halves being vertically orientedl one above the other in a common plane.

6. In a system as set forth in claim l, at least two sets of paired halves, each pair occupying a common plane and each set occupying a different plane.

7. In a system as set forth in claim 6, said different planes intersecting along a line which is Simultaneously symmetrical with respect to all of the loops in each set of pairs.

8. In a system as set forth in claim 7, a conductive supporting rod coinciding axially with said line and having two conductive plates fixed in spaced relation on said rod and normal to its axis, and a plurality of elements fixed to said plates at their outer ends and all arranged parallel to said axis and extending toward each other, the inner end of each element comprising a loop terminal and the elements being paired so that each pair together with an associated plate comprises a loop.

9. In a system as set forth in claim S, said rod being a hollow pipe and comprising the ground connection for each of said center taps, the said transformer means being supported on said pipe mid-way between said plates, and a lead-in cable conected with said transformer means and passed through said hollow pipe.

10. In a system as set forth in claim 8, said plates each comprising a disk forming the ends of a cylinder, and said elements comprising arcuate surfaces coinciding with the surface of said cylinder.

1l. In a system as set forth in claim 8, an auxiliary linear antenna disposed in alignment with the axis of said rod outside the length thereof located between said plates and receiving said signals non-directionally.

I2. In a system as set forth in claim i8, said rod supporting a housing mid-way between said plates, and said transformer means occupying said housing, said conductors being centrally fixed to said housing in insulated mutual relation and extending radially outwardly therefrom to respectively connect to said inner' ends of the elements. i

i3. In a system as set forth in claim 8, at least two dipoles forming auxiliary non-directional antennas and having theirV legs disposed parallel to said elements and interconnected at their gaps between associated legs so that all the dipole legs on the same side of the gaps with respect to one of said plates are connected together; and second transformer means connected with each of the two groups of dipole legs and to a second lead-in cable.

14. In a system as set forth in claim 13, said dipoles being arranged symmetrically with respect to said sets of paired halves.

15. In a system as set forth in claim 13, two variable condensers connected from ground to each group of dipole legs and separately adjustable to balance dipole asymmetries.

. 16. In a system as set forth in claim 13, at least'one variable condenser connected between ground and one of the groups of dipole legs and adjustable to balance out undesired asymmetries.

17. In a system as set forth in claim 13, the lengths of the dipole legs being adjustable to balance out undesired asymmetries.

18. In a system as set forth in claim 13, a separate transformer connected with each set of paired halves, and another `separate transformer connected with said auxiliary dipole antenna, each transformer being connected to a separate lead-in cable, and said lead-in cables all being substantially of the same mutual length as compared with the order of magnitude of the wave length for which the Y antenna system is designed.

References Cited in the file of this patent UNITED STATES PATENTS 1,855,184 Fisher Apr. 26, 1932 2,361,436 Taylor Oct. 31, 1944 2,485,675 Taylor et al. Oct. 26, 1949 2,576,150 Simpson Nov. 27, 1951 2,718,003 Hemphill et al Sept. 13, 1955 

